Summer Outlook

by Jan Jackson

We have just gone through a record breaking warm spell in early April. If you recall, last year we had a very warm period in April, and then the summer ended up being wetter, and cooler than normal. Can we expect the same pattern this summer?

NOAA’s Climate Prediction Center, (CPC), generates climate forecasts that cover time scales from a week, to 3 month seasons which extend out more than a year. These forecasts are located on the web at: http://www.cpc.ncep.noaa.gov/products/predictions/90day/. The forecasts predict whether temperatures and precipitation will be above, below or near normal.

The climate outlook is still being heavily influenced by the ongoing El Nino, which is a warming of the surface water in the tropical Pacific. An El Nino tends to keep the southeast U. S. cooler and wetter than normal. However, the El Nino is forecast to weaken and become neutral during the May/June/July period. Thus, the influence of El Nino on our weather should gradually go away as the summer progresses. The climate forecasts beyond the current month are in 3 month periods, or seasons.

The charts below show the temperature and precipitation forecasts for the 3 month periods beginning with May/June/July, and ending with July/August/September. For comparison, charts obtained from the PRISM Climate Group showing the monthly normals for high temperatures and precipitation for each month from May through September are also attached. PRISM is a unique knowledge-based system that uses point measurements of precipitation, temperature, and other climatic factors to produce continuous, digital grid estimates of monthly, yearly, and event-based climatic parameters. This data is located on the web here: http://www.prism.oregonstate.edu/.

Take your time and look through the charts below, but if you are in a hurry, here’s the gist of the forecast:

The overall outlook for our upcoming summer in southern West Virginia, southwest Virginia, and northwest North Carolina calls for equal chances of above, below, or near normal precipitation, and warmer than normal temperatures as we head into late summer. What “equal chances” means in regards to the precipitation forecast, is that there are no strong signals of any variability from normal.

Seasonal Temperature Outlooks from the Climate Prediction Center

May-June-July: Equal chances of above, below, or near normal temperatures.

June-July-August: Southside Virginia and all of northwest North Carolina above normal temperatures, and near normal temperatures for the rest of southwest Virginia and southern West Virginia.

July-August-September: Above normal temperatures for all of North Carolina, Virginia and West Virginia. There is also a stronger chance (40%) of above normal temperatures for western NC, including the northern mountains and foothills.

Normal High Temperatures Each Month

Normal highs in May range from 68 to 74 in most of the mountains, and from 74 to 80 east of the Blue Ridge.

Normal highs begin warming significantly in June, ranging from 74 to 80
in most of the mountains, and from 80 to 88 east of the Blue Ridge.

Normal highs in July, the warmest month for our area, range from 77 to 84
in most of the mountains, and from 84 to 92 east of the Blue Ridge.

Normal highs in August range from 77 to 84 in most of the mountains, and from 84 to 88 in most areas east of the Blue Ridge.

Normal highs begin cooling in September, but are still warmer than May. They range from
71 to 77 in most of the mountains, and from 77 to 84 in most areas east of the Blue Ridge.

Seasonal Precipitation Outlooks from the Climate Prediction Center

The precipitation outlook for May-June-July: Equal chances of above, below or near normal for our region. There is a higher chance of above normal precipitation to our south across parts of Alabama and Georgia, and much of Florida.
This is part of the lingering effects of El Nino.

The precipitation outlook for June-July-August: Again, equal chances of above, below or near normal. There is a higher of above normal just to our north from Maryland to New England.

The precipitation outlook for July-August-September: Equal chances of above, below or near normal for our area and across the eastern United States.

Normal Precipitation Each Month

The normal precipitation for May, a wet month for our area, is 4 to 5 inches for most of the area. The northwest NC Mountains, extending along the Blue Ridge into Patrick County, VA normally receives greater than 5 inches in May.

The normal precipitation for June is 4 to 5 inches for much of northwest NC, and also along the Blue Ridge in southwest VA. The normal for the rest of the area ranges from 3.2 to 4.0 inches.

The normal precipitation for July is 4 to 5 inches for all of northwest NC and most VA east of the Blue Ridge.
Most of the New River Valley and Alleghany Highlands areas of VA, also
southeast West Virginia, have a lower July precipitation of 3.2 to 4.0 inches.

The normal precipitation gets lower in August, with most of the area in the 3.2 to 4.0 inch range, except for 4.0 to 5.0 inches along the Blue Ridge, and just 2.8 to 3.2 inches for portions of the New River Valleys and southeast WV.

The focus for heavier precipitation normals in September shifts to along and east of the Blue Ridge,
which mostly ranges from 4.0 to 5.0 inches. Much of the mountains ranges from 2.8 o 4.0 inches.

Typical summer weather

Here are a few weather highlights based on local climatology studies:

Tornados developing within the WFO Blacksburg CWA usually occur between the months of April and July. There is a secondary peak of tornado touch downs in September from the remnants of tropical systems.

Severe hail (quarter sized or larger) occurs most often between the months of April and July (87%). The peak month for severe hail is May.

Severe thunderstorm wind events are most likely to occur between the months of May and August (82%), with a seasonal peak in July.

The peak month for flash flooding is June (25% of all events.)

June is also the peak month for significant flash flood events, with damages greater than $100,000.

Nearly two thirds (62%) of all flash flood events occur in the period from June through September.

September is the 2nd highest month for river flooding (tropical systems). June is the 3rd highest month for river flooding.